Double walled cryogenic tank



May 16, 1967 J. 5. CLARKE ET AL 3,319,431

DOUBLE WALLED CRYOGENIC TANK Filed May 25, 1966 4 Sheets-Sheet 1 FIG. 1

I4 E Q27; 7 |2 /|3 IY INVENTQRS JAMES S. CLARKE l9 B CHRISTOPHER E.LOESER E FQOMM ATTORNEY y 1967 .1. s. CLARKE ETAL 3,319,431

DOUBLE WALLED CRYOGENIC TANK Filed May 25, 1966 4 Sheets-Sheet 2INVENTORS q-- -l JAMES s. CLARKE Y CHRISTOPHER E. LOESER w FQJOMWATTORNEY May 16, 1967 J. 5. CLARKE ET AL DOUBLE WALLED CRYOGENIC TANK 4Sheets-Sheet Filed May 25, 1966 'oi oiic INVENTORS JAMES S CLARKE BYCHRISTOPHER E. LOESER ATTORNEY 16, 1967 J. s. CLARKE ET AL 3,319,431

DOUBLE WALLED CRYOGENIC TANK Filed May 25, 1966 4 ShetsSheet 4 INVENTORSJAMES S. CLARKE CHRISTOPHER E. LOESER ZZMF-ZAGMQ ATTORNEY United StatesPatent 3,319,431 DOUBLE WALLED CRYOGENIC TANK James S. Clarke,Cranforti, and Christopher E. Loeser, Scotch Plains, N.J., assignors toEsso Research and Engineering Company, a corporation of Delaware FiledMay 25, 1966, Ser. No. 560,034 13 Claims. (CI. 62-45) This applicationis a continuation-in-part of applicants prior copending application Ser.No. 420,998, filed Dec. 24, 1964, now abandoned.

The present invention relates in general to insulated containers for usein cargo ships adapted to transport cryogenic cargoes, such as liquefiednatural gas at atmospheric pressures. More particularly, the presentinvention relates to improvements in insulated tank structures of thedouble wall type wherein a minimum of differential expansion or thermalstress is present between the primary and secondary walls of the tank.

It has been established that the transportation of gases, such asnatural gas and the like, to remote locations may best and mostefficiently 'be accomplished by reducing the volume of the gas throughits conversion into the liquid state. Such a conversion enables thestorage volume requirements to be greatly reduced (approximatelysix-hundredfold for a given quantity of methane gas, for example) and,as should be appreciated, enables the most efl'icient transfer of thegas to a remote area.

In order to transfer liquefied gas in a practical and economical mannerin relatively large volumes, it is necessary to store the liquefied gasat approximately atmospheric pressure, since large containers built towithstand superatmospheric pressures would be impractical, if notimpossible, to construct for use on seagoing tankers or the like.However, liquefied gases maintained at atmospheric pressures haveextremely low vaporization points, ranging from about '435 F. forliquefied hydrogen to 28 F. for liquefied ammonia, and these unusuallylow temperatures of the liquids present certain problems in the designand production of insulated cargo containers. Specifically, thecontainers must be properly thermally insulated to prevent heat losseswhich would lead to excessive volatilization of the stored liquefied gasand of sufiicient strength to withstand the internal stresses that maybe induced therein by large temperature gradients through the walls ofthe container. In addition, the ship must be safeguarded againstuncontrolled flow of the low temperature liquid into contact with partsof the structure which could be damaged thereby. Accordingly, for thepurposes of increased safety and reliability and in accordance withaccepted regulatory Coast Guard codes, it has been a well-establishedpractice to provide a primary liquid-tight barrier and a secondaryliquid-tight barrier in containers used for the storage of liquefiednatural gases at cryogenic temperatures, each of which barriers isindependently capable of withstanding the thermal and hydrostaticstresses imposed by the liquefied gases.

With this requirement for a double wall insulated container, it has beenconventional to place the necessary insulation between the two walls.While this intermediate location of the insulation material assists inthe mechanical support of the inner wall, it establishes a largetemperature difference between the inner and outer walls thereby makingit necessary to provide for substantial thermally induced dimensionaldifferences 'between the two walls of the tank when the cryogenic liquidis stored.

The present invention, 'by its location of the insulation materialexterior of the outer wall of the double wall container, permits eachwall to operate at substantially the same temperature therebyeliminating the need to pro- "ice vide means for permitting dimensionalchanges therebetween.

In accordance with the principles of the present invention, therequisite multiple barrier protection is provided by a pair ofself-supporting metal tanks housed one within the other to form, ineffect, a double walled metal tank. The outer wall of the tankconstitutes a secondary liquidtight barrier and is spaced from the innerwall which constitutes a primary liquid-tight barrier. As an importantaspect of the invention, the self-supporting double walled tank may bethermally insulated by a system of insulation exterior of the outer tankwall which need not be impervious to the cargo nor able to withstand thehydrostatic pressures thereof, since the barrier requirements arefulfilled by the tank walls. Therefore, the insulating system and thedouble wall barrier system may be constructed without expansion joints,at relatively low cost, and in a vastly simplified manner in comparison,for example, with those intricate insulating systems which also serve asliquidand gas-tight barriers. Such intricate systems invariably employspecial materials and sophisticated, integral expansion joints, or theirequivalents to maintain the integrity and impermeability, i.e. thebarrier status, of the insulation.

The new and improved thermally insulated double walled tank itself isgenerally shaped to conform with the cargo hold of a tanker and may beinstalled and appropriately secured therein for expansion andcontraction, as a unit, as it is alternately chilled down and warmed upduring thermal cycling.

Accordingly, it is an important object of the present invention toprovide an improved and lower cost double wall cryogenic container notrequiring means to compensate for a differential thermal expansionbetween the inner and outer walls. I Another object of the invention isto provide an improved double wall cryogenic container which is low incost, economical in construction, and reliable in operation.

In accordance with a preferred embodiment of the in vention, a containerincludes a multiplicity of internal structural members and baflles. Thisinternal tank structure cooperates with the thermally conductivestructural means separating the primary and secondary liquid barriers toform a common and integral structural cage for the liquid barriers. Inthis way a large capacity, substantially rigid and self-supporting LNGtank is provided, for shipboard use, assuring a maximum degree ofsafety. The independent structural integrity of the container thusconstructed permits it to be keyed to the main hull of the ship so thatnormal working or flexure of the ship may occur without appreciabletransfer of such'stress to the LNG container.

Another, and therefore most important, object of the invention is toprovide a large capacity, high structural integrity, self-supporting LNGcontainer of a double-wall construction which may be mounted within aship cargo hold and substantially isolated from normal working of theships hull.

For a more complete understanding of the present invention and itsattendant advantages, reference should be made to the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a transverse cross-sectional view of a tanker in which the newand improved cryogenic container embodying the principles of theinvention has been installed;

FIG. 4 is a partially schematic horizontal plan view taken generallyalong the line 44 of FIG. 3; and

FIG. 5 is a fragmentary cross-sectional view taken along line 55 of FIG.3.

Referring to FIG. 1, the new and improved cryogenic container isinstalled in a double hulled tanker 11 (although a single hulled tankermay be suitable) having an outer hull 12 and an inner hull 13 whichdefines a cargo hold 14. Where desired or found necessary, the tanker 11may include transverse coiferdams and/or bulkheads.

The container 10 includes a closed primary barrier or inner tank of thegeneral shape of the cargo hold 14 which is fabricated from aluminum,stainless steel, high nickel steel, aluminum alloy, or a like materialwhich is capable of withstanding the thermal stresses induced by thecryogenic cargoes. In accordance with the principles of the invention,the inner tank 15, constituting a primary liquid and gas impermeablebarrier is, itself, enclosed by a similar outer tank 16, constituting asecondary barrier, also fabricated from a material such as aluminum orthe like which is not deleteriously affected by the extremely coldtemperatures of liquefied gases. As shown, the inner and outer tanks 15,16 are mutually spaced and held together as a unit by rigid spacingmembers 17 secured thereto. The spacing members 17 are sufficient insize and number to support the loaded inner tank 15 and are preferablymade of a metallic material sufficiently conductive to minimizetemperature differences between the tanks 15 and 16 during loading andunloading. Means (not shown) may be provided to fill the dead space 18between the tanks with a suitable noncombustible gas maintained at apredetermined pressure above atmosphere, where desirable or appropriate,to assure exclusion of air and moisture and to increase the safety ofthe entire container unit 10. A plurality of apertures 22 in the members17 are provided to permit the free circulation of inert gas throughoutthe spaces 18 from a single gas supply.

As an important aspect of the invention, the independent tanks 15 and16, which in effect form and may be aptly characterized as a doublewalled tank 9, are insulated with an exterior thermal insulation layer19. In this way, at the service temperature, there is essentially notemperature difference between primary tank 15, secondary tank 16, andthe interspacing members 17. Hence, it is not necessary to provide fordifferential expansion or thermal stresses between these components.This is in direct contrast to other known double wall cryogeniccontainers wherein the insulation is installed between the two walls,thus making it necessary to provide for substantial dimensionaldifferences between the two walls when the cryogenic liquid is stored inthe inner tank. Furthermore, because of its location the insulationlayer need not be self-supporting, liquid-tight, or of great strengthand may be simply and expeditiously, externally applied and secured tothe outer tank wall 16. As shown in FIG. 2, the insulation layer 19 maybe composed of abutted, individual enclosed polyurethane foam panels 20,for example, applied directly to the double wall tank 9 by an adhesive21 or other suitable means. Alternately, the insulation may be sprayedon or otherwise suitably secured to the outer wall 16. In any event, itshould be understood that the insulation chosen and its mode ofapplication to the exterior of the outer tank 16 need only be sufficientto provide adequate thermal insulation to prevent heat transfers whichwould tend to volatilize the cargo or which would tend to embrittle theship structure. Accordingly, the applied insulation need not possess theunusual strength properties and/ or high degree of dimensional stabilitythat are present in the insulation of cryogenic tanks in which theinsulation layer serves as one of the requisite liquid and vaporbarriers and, such as a barrier, often requires elaborate means forcompensation of expansion and contraction, such as expansion joints orthe like. Therefore, the cost of the insulation material and itsfabrication into an enveloping insulation layer 19 may be effectivelyreduced to a bare minimum in the system of the present invention.

As shown in FIG. 1, the insulated double walled tank 9 and itsenveloping insulation 19 are stabilized and supported as a unit withinthe cargo hold 14 by wooden blocks 23 or other appropriate means capableof withstanding the load of the tank 9 and capable of accom modatingchanges in dimension of the container unit 10, as a whole, when it issubjected to extreme variations in temperature from that of ambient whenempty to that of 260 F. when filled with a cargo of liquefied methane,for example.

It will be apparent from the foregoing that the new and improvedcryogenic tank of FIGS. 1 and 2 provides a simply constructed, yethighly reliable cargo tank which may be used to store and transportcryogenic cargoes of liquefied gases in an extremely safe and efiicientmanner. Moreover, through the employment of a new and improved,self-supporting, double walled tank in accordance with the invention,the ordinarily expensive thermal insulation system may be provided atoptimally low cost.

Referring to a further and preferred embodiment of the inventionillustrated in FIGS. 3, 4 and 5, a cross-section of a tanker includes anouter hull 102 and an inner hull 104 maintained in spaced apartrelationship by a plurality of structural members 106 in a conventionaldouble hull construction. The upper deck portions of the tanker hull arestructurally tied together by rigid C- shaped bracing members 108spanning the central or trunk portion of the tanker. Within the hold ofthe tanker vessel thus generally defined by a conventional hull is anLNG tank shown generally at 110. The tank 110 is of a rigid double wallconstruction and includes an inner skin or primary barrier 112 and anouter skin or secondary barrier 114. The primary and secondary barriers112 and 114 are separated by an air space maintained by a plurality of T-shaped braces 118 running both vertically and horizontally in egg-cratefashion. The braces 118 may include a plurality of apertures 119 (seeFIG. 5).

The base of the LNG container 110 is supported within the hold of thetanker upon a plurality of transversely running wooden beams or supportmembers 134 which are preferably of a low density and high thermalefficiency material such as balsa wood. Preferably, the beams 134 havetheir grain running vertically so that they may take a maximumcompressive load (see FIG. 5). The upper surface of each of the beams134 is in contact with the underside of the secondary barrier 114 of thetank. The lower surface of each of the beams 134 transmits the weight ofthe container and its contents to the inner hull of the ship 104. Thevertical walls of the tank 110 are keyed to the sides of the ship aswell as to the transverse cotferdams 150 by means of a key 120 engaginga corresponding keyway shown generally at 122. Accordingly, becauseslidable relative motion between the key and keyway is permissible, itwill be readily apparent from FIGS. 3 and 4 that the tank 110 maycontract and expand both in width, length and height relative to thehull as its dimensions vary due to the introduction of a low temperaturecargo therein. The exterior of the outer skin 114 is insulated with anysuitable foam type insulation system shown schematically in the figuresat 116.

Referring to the internal structure of the tank, it may be readily seenfrom FIG. 4 how the interior thereof is divided up into four generallyrectangular chambers. Each of these rectangular or quadrant chambers issimilar in configuration and for this reason only one has beenillustrated in detail. The tank 110 is divided longitudinally by a maincenter line bulkhead 124 which is substantially impervious except for avent or pressure equalization aperture 126 at a top portion thereof(FIG. 3). This impervious longitudinal bulkhead 124 therefore iselfective to prevent sloshing of the LNG material from side to sidewithin the tank. Tank 110 also includes a main transverse bulkhead 128which includes a plurality of apertures 130 to permit limited flow ofliquid fore and aft between adjacent compartments on either side of thelongitudinal bulkhead 124. Each of the bulkheads 124 and 128 arestiffened and rigidified by a plurality of structural members or webs132 as maybest be seen in FIGS. 3 and 4. In each of the four chamberswithin the tank 110 a plurality of both longitudinal and transverse webs136 are employed to further rigidity and structurally integrate theentire internal structure of each tank. The webs 136 each include a pairof upper trunk cutout portions 138 and main cutout portions designated140 to permit relatively free passage of the liquid within the tankbetween the web sections. Each of the webs 136 includes a flange portion142 about the periphery of the respective apertures 140. Extendinghorizontally across each of the four semi-separated chambers orquadrants of the tank 110 are a pair of deck or plate sectionsdesignated 144. These plate sections 144 define a substantially fiatplane adding further structural rigidity to the tank structure. Theplates 144 include a plurality of circular apertures 146 andsemi-circular apertures 148 along the longitudinal edges of each plateadjacent the longitudinal bulkhead 124 and inner skin 112 of the tank.These apertures serve to lighten the plate as well as permit relativelyfree transfer of liquid between respective levels of the tank andprovide for adequate drainage thereof. The tank 110 includes at itsbottom a pair of cargo pumps designated 152 which are shownschematically on either side of the bulkhead 124. The left hand pump iseffective to discharge fluid from the left hand chambers of tank 110through a discharge conduit represented schematically by the dotted line154. The upper end of the lines 154 exit through a batch or dome (notshown) penetrating the upper portion of the tank in the area of thetrunk. The exterior of the tank 110 is generally surrounded by arelatively large void space between the insulation 116 and the innerhull 104 of the ship. However, a plurality of anti-floatation blocks 156are provided between the underside of the deck and the upper surface ofthe tank to prevent undue movement of the tank in a vertical directionrelative to the hull structure. These anti-floatation blocks 156 arerequired to prevent undue upward movement of the tank 110 should liquidseep into the bottom of the tanker hold to in effect buoyantly supportthe tank 110. The blocks 156 may also be removed so that shouldinspection of the underside of the tank 110 be required, the entire tankmay be temporarily raised within the hold to transfer the relativelylarge void space normally occurring on the top of the tank to below thetank so that an underside inspection may be made.

Thus, it will be seen how the maze of internal bulkheads, webs,stifiening plates and deck plates within the interior of the LNG tank incombination with the plurality of vertical and horizontal T-shapedstitfeners 118 in between the inner and outer skin of the tank presentan effective and common structural cage to which the primary andsecondary barriers 112 and 114 respectively are attached. Thisstructural arrangement provides optimum rigidity and maximum safety withleast cost in this highly specialized and extreme environment ofcryogenic temperature at which the container of the invention isrequired to operate.

It should be understood that the specific structures herein illustratedand described is intended to be representative only, as certain changesmay be made therein without departing from the clear teachings of thedisclosure. For instance, while the invention finds particular utilityas a ship board cryogenic container, those skilled in the art willreadily appreciate that it may be employed to equal advantage for thesafe land-based storage of cryogenic materials. Accordingly, referenceshould be made to the following appended claims in determining the fullscope of the invention.

What is claimed is:

1. In combination, a tanker having a cargo hold of predetermined shapeand an insulated container for liquefied gases maintained atatmosphereic pressure and cryogenic temperature mounted within saidhold, said container including (a) a primary tank substantially similarin shape to said hold,

(b) a larger secondary tank substantially similar in shape to said holdand surrounding said primary tank,

(c) thermally conductive rigid structural means for maintaining saidprimary tank in fixed, spaced relation within said secondary tank andfor reducing the thermal gradient between said primary and secondarytanks when said liquefied gases are initially loaded into said containerand during transportation of said gases in said tanker,

(d) said tanks providing primary and secondary liquidtight barriers forretaining cryogenic liquefied gas cargo at atmospheric pressure, and

(e) foam insulation means applied externally and secured about saidsecondary tank in an enveloping relation therewith, said insulationmeans constituting substantially the sole insulation means of saidcontainer.

2. The combination of claim 1 including means for supporting saidcontainer within said hold for expansion and contraction as a unitrelative thereto.

3. The system of claim 2 in which (a) said primary tank and secondarytank are fabricated from material having high strength properties at lowtemperatures characteristic of stainless steel and aluminum.

4. The system of claim 2 in which (a) said insulation is permeable andof insufficient strength to withstand the hydrostatic and thermalstresses induced by liquefied gases at atmospheric pressures.

5. The system of claim 2 in which (a) said means supporting said unitinclude wooden blocks in direct contact with the exterior wall of saidsecondary tank.

6. An insulated container for storing and/ or transporting liquefiedgases at atmospheric pressures and cryogenic temperature comprising (a)a self-supporting primary tank,

(b) a self-supporting secondary tank substantially similar in shape tobut larger than said primary tank, and positioned to surround saidprimary tank in spaced relation,

(0) a plurality of thermally conductive rigid structural elementsextending between said tanks for maintaining the walls thereof in saidfixed spaced relation and for reducing the thermal gradient therebetweenwhen said container is initially loaded and subsequently filled withsaid liquefied gases,

((1) said tanks forming a cargo container including primary andsecondary liquid-tight barriers for liquid cargo,

(e) means supporting the bottom Wall of the secondary tank spaced abovea supporting surface, and

(f) foam insulation secured about and enveloping the secondary tank,said insulation constituting substantially the sole insulation aboutsaid container.

7. The container of claim 6 is further characterized by (a) saidcontainer being positioned in the hold of a ship, and

(b) the insulated container being so proportioned with respect to thehold as to provide an access space between the exterior of saidinsulated container and the interior of the hold.

8. The combination of claim including an inert gas in the space betweenthe primary and secondary tanks and wherein said structural meanscontain a plurality of apertures.

9. The combination of claim 1 including a longitudinal bulkhead withinsaid container dividing said container in substantially liquid isolatedport and starboard portions, a transverse bulkhead dividing each of saidport and starboard portions into fore and aft portions, and separatesubmerged pump means located in each of said port and starboard portionsfor pumping liquefied gases from said container.

10. The combination of claim 9 including cooperative key and keywaymeans between the exterior of said container and the interior of saidcargo hold to permit relative movement therebetween due to thermallyinduced changes in the dimensions of said container.

11. The combination of claim 10 wherein the container is supportedwithin said hold by a plurality of substantially parallel wooden beams,said beams having a vertical grain orientation to provide maximumcompressive load carrying capacity and being composed of balsa wood foroptimum thermal insulation efiiciency.

12. In combination, a tanker having a cargo hold of predetermined shapeand a container for liquefied gases maintained at atmospheric pressureand cryogenic temperature mounted within said hold, said containerincluding, an internal longitudinal bulkhead dividing said container insubstantially liquid isolated port and starboard portions, a transversebulkhead dividing each of said port and starboard portions into fore andaft portions, a plurality of apertured webs extending from side to sideof said container, a primary tank substantially similar in shape to saidhold and secured to the periphery of said webs and periphcry of eachsaid bulkhead, a plurality of stiifening structural members secured tothe exterior of said primary tank for rigidifying said tank, and alarger secondary tank substantially similar in shape to said primarytank secured to said structural members in spaced relation to saidprimary tank, said structural members in combination with each saidbulkhead and said webs providing a common structural cage for saidprimary and secondary tanks, and insulation means secured to the outersurface of said secondary tank.

13. The combination of claim 12 including cooperative key and keywaymeans between the exterior of said container and the interior of saidcargo hold to permit relative movement therebetween due to thermallyinduced changes in the dimensions of said container.

References Cited by the Examiner UNITED STATES PATENTS 2,863,297 12/1958Johnston 62-45 2,986,891 .6/1961 McMahon 62-45 3,064,612 11/1962 Gardneret al. 62-45 3,072,087 1/ 1963 Henry 62-45 3,112,043 11/1963 Tucker220-10 3,229,473 1/ 1966 Schumacher et al. 62-55 FOREIGN PATENTS 888,2471/ 1962 Great Britain.

LLOYD L. KING, Primary Examiner.

1. IN COMBINATION, A TANKER HAVING A CARGO HOLD OF PREDETERMINED SHAPEAND AN INSULATED CONTAINER FOR LIQUEFIED GASES MAINTAINED AT ATMOSPHERICPRESSURE AND CRYOGENIC TEMPERATURE MOUNTED WITHIN SAID HOLD, SAIDCONTAINER INCLUDING (A) A PRIMARY TANK SUBSTANTIALLY SIMILAR IN SHAPE TOSAID HOLD, (B) A LARGER SECONDARY TANK SUBSTANTIALLY SIMILAR IN SHAPE TOSAID HOLD AND SURROUNDING SAID PRIMARY TANK, (C) THERMALLY CONDUCTIVERIGID STRUCTURAL MEANS FOR MAINTAINING SAID PRIMARY TANK IN FIXED,SPACED RELATION WITHIN SAID SECONDARY TANK AND FOR REDUCING THE THERMALGRADIENT BETWEEN SAID PRIMARY AND SECONDARY TANKS WHEN SAID LIQUEFIEDGASES ARE INITIALLY LOADED INTO SAID CONTAINER AND DURING TRANSPORTATIONOF SAID GASES IN SAID TANKER,